Pasteurella multocida has been associated with disease in many species of animals, including man and bovine, ovine and porcine animals. It typically affects the nasopharyngeal regions and lungs of infected animals. For example, toxigenic strains of P. multocida, capsular type A or D, cause atrophic rhinitis in swine. Atrophic rhinitis (AR) results in severe necrosis of the epithelia of the upper respiratory tract as well as deformities and atrophy of the turbinates and snouts of pigs.
The pathogenicity of P. multocida is due in large part to the production of a potent necrotizing toxin, also called dermonecrotic toxin (DNT), which will be referred to hereinafter as "the toxin". The toxin has been characterized as a heat-labile protein with a molecular weight of approximately 140,000 to 160,000.
P. multocida is distinguishable from other species of Pasteurella on the basis of its growth characteristics, as follows: hemolysis: negative (90%); growth on MacConkey's agar: negative; indole production: positive; urease production: negative; and mannitol metabolism: positive. See, Zinsser, Microbiology, edit. by Joklik et al., Appleton-Century-Crofts, New York, 1980, pages 791-793, which is incorporated herein by reference.
Currently available vaccines for protecting animals from diseases associated with infection by P. multocida include inactivated toxigenic P. multocida cells, inactivated preparations of partly purified P. multocida toxin and combinations of P. multocida cell-free preparations with other inactivated P. multocida strains or B. bronchiseptica strains. [See, e.g., M. Kobisch et al, Vet. Record, 124:57-61 (1989); and N. T. Foged et al, Vet. Record, 125:7-11 (1989)]. These vaccine preparations, however, are not fully protective against disease because they fail to elicit effective amounts of the antibody that neutralizes the toxin, known as "antitoxin".
There remains a need in the art of veterinary practice for effective vaccines against infection of animals by toxigenic P. multocida.